The text of this six or so page Arabic epistle of Baha'-Allah is printed in Majmu`a-yi Hadrat- Baha'u'llah, pp. 160-166. As far as I am aware it has not been translated up till now.

Mss and printed texts:

INBMC XX

MAM : 160-166.

Translation Stephen Lambden, with select transliteration and notes.

In progress, last updated, 16-10-2015.

He is the One Who gazeth forth from His Supreme Horizon

O `Abd al-Wahhab!

Upon thee be Baha'-Allah, the Splendour of God, the Mighty, the Bestower (al-wahhab).

Hearken ye unto the Call of this Wronged One (al-mazlum)!

He calleth thee to remembrance in this prison of Acre (`Akka') for the Ocean of the All-Merciful (bahr al-rahmat) hath been manifest before all realms of Possibility (al-imkan) and the breezes of the All-Merciful (nafahat al-Rahman) are cast forth for the adherants of all religions (ahl al-adyan). So Blessed be whomsoever catcheth the fragrances of Divine Inspiration (nafahat al-wahy) and seizeth the Book (al-kitab) through a power which cometh from God, the Lord of all the worlds.

We have heard thy call through thy communication (kitab). We make mention of thee in the light of that which shall draw thee nigh unto the Horizon of the Theophany [Manifestation] (ufq al-zuhur) during these Days of God, the Mighty, the Praiseworthy. We have flung open the gate of gnosis (bab al-`irfan) through the key of the Bayan [Exposition] (miftah al-bayan) even though the people are in manifest error.